<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2017, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package	CodeIgniter
 * @author	EllisLab Dev Team
 * @copyright	Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
 * @copyright	Copyright (c) 2014 - 2017, British Columbia Institute of Technology (http://bcit.ca/)
 * @license	http://opensource.org/licenses/MIT	MIT License
 * @link	https://codeigniter.com
 * @since	Version 1.0.0
 * @filesource
 */
defined('BASEPATH') or exit('No direct script access allowed');

/**
 * Security Class
 *
 * @package CodeIgniter
 * @subpackage Libraries
 * @category Security
 * @author EllisLab Dev Team
 * @link https://codeigniter.com/user_guide/libraries/security.html
 */
class CI_Security
{

    /**
     * List of sanitize filename strings
     *
     * @var array
     */
    public $filename_bad_chars = array(
        '../',
        '<!--',
        '-->',
        '<',
        '>',
        "'",
        '"',
        '&',
        '$',
        '#',
        '{',
        '}',
        '[',
        ']',
        '=',
        ';',
        '?',
        '%20',
        '%22',
        '%3c', // <
        '%253c', // <
        '%3e', // >
        '%0e', // >
        '%28', // (
        '%29', // )
        '%2528', // (
        '%26', // &
        '%24', // $
        '%3f', // ?
        '%3b', // ;
        '%3d'
    ) // =
;

    /**
     * Character set
     *
     * Will be overridden by the constructor.
     *
     * @var string
     */
    public $charset = 'UTF-8';

    /**
     * XSS Hash
     *
     * Random Hash for protecting URLs.
     *
     * @var string
     */
    protected $_xss_hash;

    /**
     * CSRF Hash
     *
     * Random hash for Cross Site Request Forgery protection cookie
     *
     * @var string
     */
    protected $_csrf_hash;

    /**
     * CSRF Expire time
     *
     * Expiration time for Cross Site Request Forgery protection cookie.
     * Defaults to two hours (in seconds).
     *
     * @var int
     */
    protected $_csrf_expire = 7200;

    /**
     * CSRF Token name
     *
     * Token name for Cross Site Request Forgery protection cookie.
     *
     * @var string
     */
    protected $_csrf_token_name = 'ci_csrf_token';

    /**
     * CSRF Cookie name
     *
     * Cookie name for Cross Site Request Forgery protection cookie.
     *
     * @var string
     */
    protected $_csrf_cookie_name = 'ci_csrf_token';

    /**
     * List of never allowed strings
     *
     * @var array
     */
    protected $_never_allowed_str = array(
        'document.cookie' => '[removed]',
        'document.write' => '[removed]',
        '.parentNode' => '[removed]',
        '.innerHTML' => '[removed]',
        '-moz-binding' => '[removed]',
        '<!--' => '&lt;!--',
        '-->' => '--&gt;',
        '<![CDATA[' => '&lt;![CDATA[',
        '<comment>' => '&lt;comment&gt;',
        '<%' => '&lt;&#37;'
    );

    /**
     * List of never allowed regex replacements
     *
     * @var array
     */
    protected $_never_allowed_regex = array(
        'javascript\s*:',
        '(document|(document\.)?window)\.(location|on\w*)',
        'expression\s*(\(|&\#40;)', // CSS and IE
        'vbscript\s*:', // IE, surprise!
        'wscript\s*:', // IE
        'jscript\s*:', // IE
        'vbs\s*:', // IE
        'Redirect\s+30\d',
        "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?"
    );

    /**
     * Class constructor
     *
     * @return void
     */
    public function __construct()
    {
        // Is CSRF protection enabled?
        if (config_item('csrf_protection')) {
            // CSRF config
            foreach (array(
                'csrf_expire',
                'csrf_token_name',
                'csrf_cookie_name'
            ) as $key) {
                if (NULL !== ($val = config_item($key))) {
                    $this->{'_' . $key} = $val;
                }
            }
            
            // Append application specific cookie prefix
            if ($cookie_prefix = config_item('cookie_prefix')) {
                $this->_csrf_cookie_name = $cookie_prefix . $this->_csrf_cookie_name;
            }
            
            // Set the CSRF hash
            $this->_csrf_set_hash();
        }
        
        $this->charset = strtoupper(config_item('charset'));
        
        log_message('info', 'Security Class Initialized');
    }
    
    // --------------------------------------------------------------------
    
    /**
     * CSRF Verify
     *
     * @return CI_Security
     */
    public function csrf_verify()
    {
        // If it's not a POST request we will set the CSRF cookie
        if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST') {
            return $this->csrf_set_cookie();
        }
        
        // Check if URI has been whitelisted from CSRF checks
        if ($exclude_uris = config_item('csrf_exclude_uris')) {
            $uri = load_class('URI', 'core');
            foreach ($exclude_uris as $excluded) {
                if (preg_match('#^' . $excluded . '$#i' . (UTF8_ENABLED ? 'u' : ''), $uri->uri_string())) {
                    return $this;
                }
            }
        }
        
        // Check CSRF token validity, but don't error on mismatch just yet - we'll want to regenerate
        $valid = isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]) && hash_equals($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]);
        
        // We kill this since we're done and we don't want to pollute the _POST array
        unset($_POST[$this->_csrf_token_name]);
        
        // Regenerate on every submission?
        if (config_item('csrf_regenerate')) {
            // Nothing should last forever
            unset($_COOKIE[$this->_csrf_cookie_name]);
            $this->_csrf_hash = NULL;
        }
        
        $this->_csrf_set_hash();
        $this->csrf_set_cookie();
        
        if ($valid !== TRUE) {
            $this->csrf_show_error();
        }
        
        log_message('info', 'CSRF token verified');
        return $this;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * CSRF Set Cookie
     *
     * @codeCoverageIgnore
     * 
     * @return CI_Security
     */
    public function csrf_set_cookie()
    {
        $expire = time() + $this->_csrf_expire;
        $secure_cookie = (bool) config_item('cookie_secure');
        
        if ($secure_cookie && ! is_https()) {
            return FALSE;
        }
        
        setcookie($this->_csrf_cookie_name, $this->_csrf_hash, $expire, config_item('cookie_path'), config_item('cookie_domain'), $secure_cookie, config_item('cookie_httponly'));
        log_message('info', 'CSRF cookie sent');
        
        return $this;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Show CSRF Error
     *
     * @return void
     */
    public function csrf_show_error()
    {
        show_error('The action you have requested is not allowed.', 403);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Get CSRF Hash
     *
     * @see CI_Security::$_csrf_hash
     * @return string hash
     */
    public function get_csrf_hash()
    {
        return $this->_csrf_hash;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Get CSRF Token Name
     *
     * @see CI_Security::$_csrf_token_name
     * @return string token name
     */
    public function get_csrf_token_name()
    {
        return $this->_csrf_token_name;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * XSS Clean
     *
     * Sanitizes data so that Cross Site Scripting Hacks can be
     * prevented. This method does a fair amount of work but
     * it is extremely thorough, designed to prevent even the
     * most obscure XSS attempts. Nothing is ever 100% foolproof,
     * of course, but I haven't been able to get anything passed
     * the filter.
     *
     * Note: Should only be used to deal with data upon submission.
     * It's not something that should be used for general
     * runtime processing.
     *
     * @link http://channel.bitflux.ch/wiki/XSS_Prevention
     *       Based in part on some code and ideas from Bitflux.
     *      
     * @link http://ha.ckers.org/xss.html
     *       To help develop this script I used this great list of
     *       vulnerabilities along with a few other hacks I've
     *       harvested from examining vulnerabilities in other programs.
     *      
     * @param string|string[] $str            
     * @param bool $is_image
     *            input is an image
     * @return string
     */
    public function xss_clean($str, $is_image = FALSE)
    {
        // Is the string an array?
        if (is_array($str)) {
            while (list ($key) = each($str)) {
                $str[$key] = $this->xss_clean($str[$key]);
            }
            
            return $str;
        }
        
        // Remove Invisible Characters
        $str = remove_invisible_characters($str);
        
        /*
         * URL Decode
         *
         * Just in case stuff like this is submitted:
         *
         * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
         *
         * Note: Use rawurldecode() so it does not remove plus signs
         */
        if (stripos($str, '%') !== false) {
            do {
                $oldstr = $str;
                $str = rawurldecode($str);
                $str = preg_replace_callback('#%(?:\s*[0-9a-f]){2,}#i', array(
                    $this,
                    '_urldecodespaces'
                ), $str);
            } while ($oldstr !== $str);
            unset($oldstr);
        }
        
        /*
         * Convert character entities to ASCII
         *
         * This permits our tests below to work reliably.
         * We only convert entities that are within tags since
         * these are the ones that will pose security problems.
         */
        $str = preg_replace_callback("/[^a-z0-9>]+[a-z0-9]+=([\'\"]).*?\\1/si", array(
            $this,
            '_convert_attribute'
        ), $str);
        $str = preg_replace_callback('/<\w+.*/si', array(
            $this,
            '_decode_entity'
        ), $str);
        
        // Remove Invisible Characters Again!
        $str = remove_invisible_characters($str);
        
        /*
         * Convert all tabs to spaces
         *
         * This prevents strings like this: ja vascript
         * NOTE: we deal with spaces between characters later.
         * NOTE: preg_replace was found to be amazingly slow here on
         * large blocks of data, so we use str_replace.
         */
        $str = str_replace("\t", ' ', $str);
        
        // Capture converted string for later comparison
        $converted_string = $str;
        
        // Remove Strings that are never allowed
        $str = $this->_do_never_allowed($str);
        
        /*
         * Makes PHP tags safe
         *
         * Note: XML tags are inadvertently replaced too:
         *
         * <?xml
         *
         * But it doesn't seem to pose a problem.
         */
        if ($is_image === TRUE) {
            // Images have a tendency to have the PHP short opening and
            // closing tags every so often so we skip those and only
            // do the long opening tags.
            $str = preg_replace('/<\?(php)/i', '&lt;?\\1', $str);
        } else {
            $str = str_replace(array(
                '<?',
                '?' . '>'
            ), array(
                '&lt;?',
                '?&gt;'
            ), $str);
        }
        
        /*
         * Compact any exploded words
         *
         * This corrects words like: j a v a s c r i p t
         * These words are compacted back to their correct state.
         */
        $words = array(
            'javascript',
            'expression',
            'vbscript',
            'jscript',
            'wscript',
            'vbs',
            'script',
            'base64',
            'applet',
            'alert',
            'document',
            'write',
            'cookie',
            'window',
            'confirm',
            'prompt',
            'eval'
        );
        
        foreach ($words as $word) {
            $word = implode('\s*', str_split($word)) . '\s*';
            
            // We only want to do this when it is followed by a non-word character
            // That way valid stuff like "dealer to" does not become "dealerto"
            $str = preg_replace_callback('#(' . substr($word, 0, - 3) . ')(\W)#is', array(
                $this,
                '_compact_exploded_words'
            ), $str);
        }
        
        /*
         * Remove disallowed Javascript in links or img tags
         * We used to do some version comparisons and use of stripos(),
         * but it is dog slow compared to these simplified non-capturing
         * preg_match(), especially if the pattern exists in the string
         *
         * Note: It was reported that not only space characters, but all in
         * the following pattern can be parsed as separators between a tag name
         * and its attributes: [\d\s"\'`;,\/\=\(\x00\x0B\x09\x0C]
         * ... however, remove_invisible_characters() above already strips the
         * hex-encoded ones, so we'll skip them below.
         */
        do {
            $original = $str;
            
            if (preg_match('/<a/i', $str)) {
                $str = preg_replace_callback('#<a(?:rea)?[^a-z0-9>]+([^>]*?)(?:>|$)#si', array(
                    $this,
                    '_js_link_removal'
                ), $str);
            }
            
            if (preg_match('/<img/i', $str)) {
                $str = preg_replace_callback('#<img[^a-z0-9]+([^>]*?)(?:\s?/?>|$)#si', array(
                    $this,
                    '_js_img_removal'
                ), $str);
            }
            
            if (preg_match('/script|xss/i', $str)) {
                $str = preg_replace('#</*(?:script|xss).*?>#si', '[removed]', $str);
            }
        } while ($original !== $str);
        unset($original);
        
        /*
         * Sanitize naughty HTML elements
         *
         * If a tag containing any of the words in the list
         * below is found, the tag gets converted to entities.
         *
         * So this: <blink>
         * Becomes: &lt;blink&gt;
         */
        $pattern = '#' . '<((?<slash>/*\s*)((?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)|.+)' . // tag start and name, followed by a non-tag character
'[^\s\042\047a-z0-9>/=]*' . // a valid attribute character immediately after the tag would count as a separator
                                   // optional attributes
        '(?<attributes>(?:[\s\042\047/=]*' . // non-attribute characters, excluding > (tag close) for obvious reasons
'[^\s\042\047>/=]+' . // attribute characters
                             // optional attribute-value
        '(?:\s*=' . // attribute-value separator
'(?:[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*))' . // single, double or non-quoted value
')?' . // end optional attribute-value group
')*)' . // end optional attributes group
'[^>]*)(?<closeTag>\>)?#isS';
        
        // Note: It would be nice to optimize this for speed, BUT
        // only matching the naughty elements here results in
        // false positives and in turn - vulnerabilities!
        do {
            $old_str = $str;
            $str = preg_replace_callback($pattern, array(
                $this,
                '_sanitize_naughty_html'
            ), $str);
        } while ($old_str !== $str);
        unset($old_str);
        
        /*
         * Sanitize naughty scripting elements
         *
         * Similar to above, only instead of looking for
         * tags it looks for PHP and JavaScript commands
         * that are disallowed. Rather than removing the
         * code, it simply converts the parenthesis to entities
         * rendering the code un-executable.
         *
         * For example: eval('some code')
         * Becomes: eval&#40;'some code'&#41;
         */
        $str = preg_replace('#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', '\\1\\2&#40;\\3&#41;', $str);
        
        // Final clean up
        // This adds a bit of extra precaution in case
        // something got through the above filters
        $str = $this->_do_never_allowed($str);
        
        /*
         * Images are Handled in a Special Way
         * - Essentially, we want to know that after all of the character
         * conversion is done whether any unwanted, likely XSS, code was found.
         * If not, we return TRUE, as the image is clean.
         * However, if the string post-conversion does not matched the
         * string post-removal of XSS, then it fails, as there was unwanted XSS
         * code found and removed/changed during processing.
         */
        if ($is_image === TRUE) {
            return ($str === $converted_string);
        }
        
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * XSS Hash
     *
     * Generates the XSS hash if needed and returns it.
     *
     * @see CI_Security::$_xss_hash
     * @return string hash
     */
    public function xss_hash()
    {
        if ($this->_xss_hash === NULL) {
            $rand = $this->get_random_bytes(16);
            $this->_xss_hash = ($rand === FALSE) ? md5(uniqid(mt_rand(), TRUE)) : bin2hex($rand);
        }
        
        return $this->_xss_hash;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Get random bytes
     *
     * @param int $length            
     * @return string
     */
    public function get_random_bytes($length)
    {
        if (empty($length) or ! ctype_digit((string) $length)) {
            return FALSE;
        }
        
        if (function_exists('random_bytes')) {
            try {
                // The cast is required to avoid TypeError
                return random_bytes((int) $length);
            } catch (Exception $e) {
                // If random_bytes() can't do the job, we can't either ...
                // There's no point in using fallbacks.
                log_message('error', $e->getMessage());
                return FALSE;
            }
        }
        
        // Unfortunately, none of the following PRNGs is guaranteed to exist ...
        if (defined('MCRYPT_DEV_URANDOM') && ($output = mcrypt_create_iv($length, MCRYPT_DEV_URANDOM)) !== FALSE) {
            return $output;
        }
        
        if (is_readable('/dev/urandom') && ($fp = fopen('/dev/urandom', 'rb')) !== FALSE) {
            // Try not to waste entropy ...
            is_php('5.4') && stream_set_chunk_size($fp, $length);
            $output = fread($fp, $length);
            fclose($fp);
            if ($output !== FALSE) {
                return $output;
            }
        }
        
        if (function_exists('openssl_random_pseudo_bytes')) {
            return openssl_random_pseudo_bytes($length);
        }
        
        return FALSE;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * HTML Entities Decode
     *
     * A replacement for html_entity_decode()
     *
     * The reason we are not using html_entity_decode() by itself is because
     * while it is not technically correct to leave out the semicolon
     * at the end of an entity most browsers will still interpret the entity
     * correctly. html_entity_decode() does not convert entities without
     * semicolons, so we are left with our own little solution here. Bummer.
     *
     * @link http://php.net/html-entity-decode
     *      
     * @param string $str            
     * @param string $charset            
     * @return string
     */
    public function entity_decode($str, $charset = NULL)
    {
        if (strpos($str, '&') === FALSE) {
            return $str;
        }
        
        static $_entities;
        
        isset($charset) or $charset = $this->charset;
        $flag = is_php('5.4') ? ENT_COMPAT | ENT_HTML5 : ENT_COMPAT;
        
        if (! isset($_entities)) {
            $_entities = array_map('strtolower', get_html_translation_table(HTML_ENTITIES, $flag, $charset));
            
            // If we're not on PHP 5.4+, add the possibly dangerous HTML 5
            // entities to the array manually
            if ($flag === ENT_COMPAT) {
                $_entities[':'] = '&colon;';
                $_entities['('] = '&lpar;';
                $_entities[')'] = '&rpar;';
                $_entities["\n"] = '&NewLine;';
                $_entities["\t"] = '&Tab;';
            }
        }
        
        do {
            $str_compare = $str;
            
            // Decode standard entities, avoiding false positives
            if (preg_match_all('/&[a-z]{2,}(?![a-z;])/i', $str, $matches)) {
                $replace = array();
                $matches = array_unique(array_map('strtolower', $matches[0]));
                foreach ($matches as &$match) {
                    if (($char = array_search($match . ';', $_entities, TRUE)) !== FALSE) {
                        $replace[$match] = $char;
                    }
                }
                
                $str = str_replace(array_keys($replace), array_values($replace), $str);
            }
            
            // Decode numeric & UTF16 two byte entities
            $str = html_entity_decode(preg_replace('/(&#(?:x0*[0-9a-f]{2,5}(?![0-9a-f;])|(?:0*\d{2,4}(?![0-9;]))))/iS', '$1;', $str), $flag, $charset);
            
            if ($flag === ENT_COMPAT) {
                $str = str_replace(array_values($_entities), array_keys($_entities), $str);
            }
        } while ($str_compare !== $str);
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Sanitize Filename
     *
     * @param string $str
     *            name
     * @param bool $relative_path
     *            preserve paths
     * @return string
     */
    public function sanitize_filename($str, $relative_path = FALSE)
    {
        $bad = $this->filename_bad_chars;
        
        if (! $relative_path) {
            $bad[] = './';
            $bad[] = '/';
        }
        
        $str = remove_invisible_characters($str, FALSE);
        
        do {
            $old = $str;
            $str = str_replace($bad, '', $str);
        } while ($old !== $str);
        
        return stripslashes($str);
    }
    
    // ----------------------------------------------------------------
    
    /**
     * Strip Image Tags
     *
     * @param string $str            
     * @return string
     */
    public function strip_image_tags($str)
    {
        return preg_replace(array(
            '#<img[\s/]+.*?src\s*=\s*(["\'])([^\\1]+?)\\1.*?\>#i',
            '#<img[\s/]+.*?src\s*=\s*?(([^\s"\'=<>`]+)).*?\>#i'
        ), '\\2', $str);
    }
    
    // ----------------------------------------------------------------
    
    /**
     * URL-decode taking spaces into account
     *
     * @see https://github.com/bcit-ci/CodeIgniter/issues/4877
     * @param array $matches            
     * @return string
     */
    protected function _urldecodespaces($matches)
    {
        $input = $matches[0];
        $nospaces = preg_replace('#\s+#', '', $input);
        return ($nospaces === $input) ? $input : rawurldecode($nospaces);
    }
    
    // ----------------------------------------------------------------
    
    /**
     * Compact Exploded Words
     *
     * Callback method for xss_clean() to remove whitespace from
     * things like 'j a v a s c r i p t'.
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $matches            
     * @return string
     */
    protected function _compact_exploded_words($matches)
    {
        return preg_replace('/\s+/s', '', $matches[1]) . $matches[2];
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Sanitize Naughty HTML
     *
     * Callback method for xss_clean() to remove naughty HTML elements.
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $matches            
     * @return string
     */
    protected function _sanitize_naughty_html($matches)
    {
        static $naughty_tags = array(
            'alert',
            'area',
            'prompt',
            'confirm',
            'applet',
            'audio',
            'basefont',
            'base',
            'behavior',
            'bgsound',
            'blink',
            'body',
            'embed',
            'expression',
            'form',
            'frameset',
            'frame',
            'head',
            'html',
            'ilayer',
            'iframe',
            'input',
            'button',
            'select',
            'isindex',
            'layer',
            'link',
            'meta',
            'keygen',
            'object',
            'plaintext',
            'style',
            'script',
            'textarea',
            'title',
            'math',
            'video',
            'svg',
            'xml',
            'xss'
        );
        
        static $evil_attributes = array(
            'on\w+',
            'style',
            'xmlns',
            'formaction',
            'form',
            'xlink:href',
            'FSCommand',
            'seekSegmentTime'
        );
        
        // First, escape unclosed tags
        if (empty($matches['closeTag'])) {
            return '&lt;' . $matches[1];
        }        // Is the element that we caught naughty? If so, escape it
        elseif (in_array(strtolower($matches['tagName']), $naughty_tags, TRUE)) {
            return '&lt;' . $matches[1] . '&gt;';
        }        // For other tags, see if their attributes are "evil" and strip those
        elseif (isset($matches['attributes'])) {
            // We'll store the already fitlered attributes here
            $attributes = array();
            
            // Attribute-catching pattern
            $attributes_pattern = '#' . '(?<name>[^\s\042\047>/=]+)' . // attribute characters
                                          // optional attribute-value
            '(?:\s*=(?<value>[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*)))' . // attribute-value separator
'#i';
            
            // Blacklist pattern for evil attribute names
            $is_evil_pattern = '#^(' . implode('|', $evil_attributes) . ')$#i';
            
            // Each iteration filters a single attribute
            do {
                // Strip any non-alpha characters that may preceed an attribute.
                // Browsers often parse these incorrectly and that has been a
                // of numerous XSS issues we've had.
                $matches['attributes'] = preg_replace('#^[^a-z]+#i', '', $matches['attributes']);
                
                if (! preg_match($attributes_pattern, $matches['attributes'], $attribute, PREG_OFFSET_CAPTURE)) {
                    // No (valid) attribute found? Discard everything else inside the tag
                    break;
                }
                
                if (
                // Is it indeed an "evil" attribute?
                preg_match($is_evil_pattern, $attribute['name'][0]) or 
                // Or does it have an equals sign, but no value and not quoted? Strip that too!
                (trim($attribute['value'][0]) === '')) {
                    $attributes[] = 'xss=removed';
                } else {
                    $attributes[] = $attribute[0][0];
                }
                
                $matches['attributes'] = substr($matches['attributes'], $attribute[0][1] + strlen($attribute[0][0]));
            } while ($matches['attributes'] !== '');
            
            $attributes = empty($attributes) ? '' : ' ' . implode(' ', $attributes);
            return '<' . $matches['slash'] . $matches['tagName'] . $attributes . '>';
        }
        
        return $matches[0];
    }
    
    // --------------------------------------------------------------------
    
    /**
     * JS Link Removal
     *
     * Callback method for xss_clean() to sanitize links.
     *
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on link-heavy strings.
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $match            
     * @return string
     */
    protected function _js_link_removal($match)
    {
        return str_replace($match[1], preg_replace('#href=.*?(?:(?:alert|prompt|confirm)(?:\(|&\#40;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|d\s*a\s*t\s*a\s*:)#si', '', $this->_filter_attributes($match[1])), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * JS Image Removal
     *
     * Callback method for xss_clean() to sanitize image tags.
     *
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on image tag heavy strings.
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $match            
     * @return string
     */
    protected function _js_img_removal($match)
    {
        return str_replace($match[1], preg_replace('#src=.*?(?:(?:alert|prompt|confirm|eval)(?:\(|&\#40;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si', '', $this->_filter_attributes($match[1])), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Attribute Conversion
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $match            
     * @return string
     */
    protected function _convert_attribute($match)
    {
        return str_replace(array(
            '>',
            '<',
            '\\'
        ), array(
            '&gt;',
            '&lt;',
            '\\\\'
        ), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Filter Attributes
     *
     * Filters tag attributes for consistency and safety.
     *
     * @used-by CI_Security::_js_img_removal()
     * @used-by CI_Security::_js_link_removal()
     * 
     * @param string $str            
     * @return string
     */
    protected function _filter_attributes($str)
    {
        $out = '';
        if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches)) {
            foreach ($matches[0] as $match) {
                $out .= preg_replace('#/\*.*?\*/#s', '', $match);
            }
        }
        
        return $out;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * HTML Entity Decode Callback
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param array $match            
     * @return string
     */
    protected function _decode_entity($match)
    {
        // Protect GET variables in URLs
        // 901119URL5918AMP18930PROTECT8198
        $match = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-/]+)|i', $this->xss_hash() . '\\1=\\2', $match[0]);
        
        // Decode, then un-protect URL GET vars
        return str_replace($this->xss_hash(), '&', $this->entity_decode($match, $this->charset));
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Do Never Allowed
     *
     * @used-by CI_Security::xss_clean()
     * 
     * @param
     *            string
     * @return string
     */
    protected function _do_never_allowed($str)
    {
        $str = str_replace(array_keys($this->_never_allowed_str), $this->_never_allowed_str, $str);
        
        foreach ($this->_never_allowed_regex as $regex) {
            $str = preg_replace('#' . $regex . '#is', '[removed]', $str);
        }
        
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Set CSRF Hash and Cookie
     *
     * @return string
     */
    protected function _csrf_set_hash()
    {
        if ($this->_csrf_hash === NULL) {
            // If the cookie exists we will use its value.
            // We don't necessarily want to regenerate it with
            // each page load since a page could contain embedded
            // sub-pages causing this feature to fail
            if (isset($_COOKIE[$this->_csrf_cookie_name]) && is_string($_COOKIE[$this->_csrf_cookie_name]) && preg_match('#^[0-9a-f]{32}$#iS', $_COOKIE[$this->_csrf_cookie_name]) === 1) {
                return $this->_csrf_hash = $_COOKIE[$this->_csrf_cookie_name];
            }
            
            $rand = $this->get_random_bytes(16);
            $this->_csrf_hash = ($rand === FALSE) ? md5(uniqid(mt_rand(), TRUE)) : bin2hex($rand);
        }
        
        return $this->_csrf_hash;
    }
}
